1. Field of Endeavor
The present invention relates to generators for generating electrical energy, and more specifically to turbogenerator rotors.
2. Brief Description of the Related Art
For a long time it has been known to produce rotors of large turbomachines, such as steam turbines or gas turbines, from individual rotor elements which are welded together to form a unit (see, for example, EP A1-0 604 754). As a result of this, it is possible, inter alia, to produce the thermally differently stressed sections of the rotor from different materials, and to optimize the sections of the rotor with regard to cost and stability. Also, in the case of materials purchasing, it is simpler to procure comparatively small disk-shaped elements than to procure a specially manufactured and formed monoblock.
With the rotors of electric generators, especially turbogenerators, the production of the rotor by welding together individual disk-shaped elements up to now has not been enforced. With rotors of turbogenerators, in addition to the mechanical and thermal characteristics, attention is also to be paid to the magnetic and electrical characteristics because the rotors are part of a magnetic circuit and customarily carry a winding. For accommodating the winding, slots, which extend in the axial direction, are provided in the body of the rotor and are radially let into the inside of the rotor with a certain slot depth (see, for example, EP 1 361 642).
Rotors, which are assembled from individual disks, of turbogenerators have at times been proposed in the past: A rotor for turbogenerators, which is assembled from solid disks which are arranged in series axially next to each, is known from DE Patent No. 573 512. The end disks are produced in one piece with the shaft end pieces. The disks are connected to one another on their circumferences by means of weld seams. For supporting the weld seams, it can be advantageous to additionally connect the disks to one another by means of bolts. For stabilization, the disk faces can also be provided in an alternating manner with projections and recesses which interlock.
For increasing the strength, weld seams can also be provided along the winding slots which are cut into the circumference of the rotor. In this case, it is disadvantageous that the narrow weld seams which are restricted to the edge, especially if they are still broken by the winding slots, enable only a limited strength of the welded rotor. Additional weld seams in the slots certainly increase the strength to a certain extent, but are to be realized only at high cost.
A rotor for a turbogenerator is furthermore known from U.S. Pat. No. 3,780,428, in which the rotor body is also constructed by welding along the edges of a number of disks. In this case, additional strength is imparted to the narrow weld seams by the end pieces of the rotor being connected by means of an internal bolt which puts the rotor under compressive strain in the axial direction. Also, these measures for increasing the strength are extremely costly and lead to a very complex construction of the rotor.
Rotors of turbogenerators with deep weld seams have also already been proposed in the past (see DE-B-1-017 263).
In light of a resurgent nuclear business, large rotors (4-pole turbogenerators, individual weight of the generator rotor of up to 300 tons) are again called for. Such large forgings can only be manufactured worldwide by a few vendors to order. A reject risk exists, which possibly can only be established in the subsequent machining state.
Sometimes, with increasing sizes and increasing weight of the forging, inhomogeneities occur with regard to physical characteristics and manufacturing-dependent residual stresses. Smaller forgings, however, can be completely forged very well and hardly any risk is run of the rotor being twisted during the finish process as a result of asymmetries in the material structure.